Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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What exactly is a quantum of light?

I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a photon as a quantum of light, which it further explains as some kind of a wave-packet. What ...
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3answers
14k views

Is it possible to reproduce Double-slit experiment by myself at home?

I want to reproduce this experiment by myself. What I need for this. What parameters of slits and laser/another light source it needs? Is it possible to make DIY-detector?
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1answer
600 views

Is colour, as represented using primary colours, accurate only to humans?

Slightly biological, hopefully physical enough to be answered. Suppose a magenta hue is represented by a mix of red and blue pigment. This is all very well for a creature with red and blue ...
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2answers
879 views

Why fast eye movement splits a white LED into the RGB components?

I have a "white" LED as the notification light on my phone. When I look at it straight it looks whitish, but when I move my eyes around (or shake my head) I suddenly see glimpses of red and green (and ...
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3answers
2k views

Why isn't light scattered through transparency?

I'm asking a question that has bothered me for years and years. First of all, let me give some context. I'm a layman in physics (college educated, math major). I've read Feynman's QED cover to cover, ...
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1answer
498 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
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4answers
6k views

What happens when a photon hits a mirror?

When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
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2answers
774 views

Sun spectroscopy - Home experiment

We let the sun light run through a 5x3x3cm triangular glass prism and we examined the formed 'rainbow' in search of Fraunhofer lines. However, even though we looked close enough (even with a ...
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3answers
7k views

Why do green lasers appear brighter and stronger than red and blue lasers?

This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I ...
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3answers
2k views

How come light waves don't get caught and absorbed by the electrons of oxygen atoms in the in air?

Shouldn't air be opaque since instead of coming into our eye, the lightwaves get caught in the electrons? If oxygen does absorb light waves, how come air is not hot and you can see through it? The way ...
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3answers
653 views

What gives things color? [duplicate]

I know that color comes from things not absorbing a certain wavelength of light, but what property gives something color? Like what property of copper atoms makes copper as a whole brown, or cobalt ...
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3answers
1k views

What causes atoms to have their specific colors?

I understand that light (color) is part of the electromagnetic spectrum, and that it depends on what wavelengths are reflected/absorbed. Though what property of an individual atom gives it its color? ...
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4answers
962 views

How does interference move energy from destructive to constructive regions?

I recently read (sorry but I don’t have a reference) that interference is not only about destructive and constructive interference but moving energy from destructive to constructive regions according ...
12
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1answer
471 views

Why can I turn light red or blue by holding my finger up to it?

This is a difficult phenomenon to explain. Imagine you have an opaque object partially covering a very bright light source, for example, an object held up against the sky. The left hand diagram is ...
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6answers
558 views

How large is the universe?

We know that the age of the universe (or, at least the time since the Big Bang) is roughly 13.75 billion years. I have heard that the size of the universe is much larger than what we can see, in other ...
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1answer
532 views

Looking at an iPhone through a Polarizer

Maybe this is more of an Electrical Engineering question, but does anyone know why iPhones looking green/red through a linear polarizer? I find it strange that the light coming out would be ...
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4answers
433 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...
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4answers
540 views

Does the speed of medium affect the path of light?

Let's say I shine a laser from a stationary medium into a moving medium (suppose the water is moving very quickly) perpendicular to the interface and back to a stationary medium like this: (Note: ...
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2answers
368 views

What mechanisms allow conductors to be transparent?

An electric field in a conductor causes charges to redistribute so as to cancel out the original field, bringing the field to zero. This is, I think, a common argument for why conductors are generally ...
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5answers
5k views

What happens to light and mass in the center of a black hole?

I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black ...
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1answer
751 views

Why Do My Fan Blades Produce Color When They Spin?

I've posted a short video here as a visual aid. Whenever I put my fan on Medium speed during the night time, it produces a rotating Blue and Orange color design, despite both fan blades being a white ...
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2answers
1k views

EM wave function & photon wavefunction

According to this review Photon wave function. Iwo Bialynicki-Birula. Progress in Optics 36 V (1996), pp. 245-294. arXiv:quant-ph/0508202, a classical EM plane wavefunction is a wavefunction (in ...
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1answer
332 views

What causes the sharp borderline at the bottom of northern lights?

The northern lights are caused by cosmic charged particles interacting with the earth's upper atmoshphere. The particles can be trapped by the Lorentz force, so that we can see them where the magnetic ...
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1answer
270 views

Why do some sunsets have a green flash?

Some sunsets exhibit a phenomenon called "green flash," where there is a quick flash of green light right as the sun is setting. I have seen this myself several times, and sort of understand it. I am ...
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6answers
2k views

Light's inverse square law: Does it require a minimum distance from the source?

Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
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4answers
1k views

Why doesn't more light bounce off of things in the manner of sound?

If I'm sitting in the den with my door slightly cracked, I can hear my wife washing dishes in the kitchen down the hall. But why can't I also 'see' images of her washing dishes if, say, I looked up on ...
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4answers
9k views

Can someone explain the color Pink to me?

I just finished watching this interesting video: http://youtu.be/S9dqJRyk0YM It does a very quick explanation of how pink light doesn't exist, and that the concept of pink is our brain's attempt at ...
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3answers
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What is the color of a mirror?

A mirror couldn't be white, as then you wouldn't be able to see your reflection so clearly. It wouldn't be transparent, as that then won't reflect. So what color is it?
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5answers
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Where does light go after it enters a black hole?

Nothing passes through a black hole. Where do things go then? If light enters a black hole, what happens to it? Do things go to a white hole and resume in another universe?
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3answers
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Why do stars flicker?

Why do stars flicker and planets don't? At least this is what I've read online and seen on the night sky. I've heard that it has to do something with the fact that stars emit light and planets reflect ...
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5answers
3k views

What happens to light after it enters an eye

What happens to the light [energy] after it enters an eye and hits the rods and cones? I presume the energy becomes electrical, and it must be near 100% perfect, else our eyes would heat up? Or am I ...
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2answers
958 views

Why does the sky suddenly look gray through this window?

I am looking to the windowed roof of my building, and I notice that the sky, which has few white clouds, sometimes looks completely gray, as if there was a huge cover of gray clouds, but there are ...
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5answers
2k views

Can someone explain the science behind MIT's 230% efficient LEDs?

I was reading Gizmodo the other day and I didn't quite understand the Physics behind this. Could anybody shed some light on how this effect actually works?
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3answers
779 views

Using a black hole as a mirror?

http://www.youtube.com/watch?v=ENd8Sz0AFOk The YouTube video is a good example how the gravity of this merging binary black holes bend light around themselves.
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1answer
54 views

Glowing light around my shadow during sunrise

This morning I was jogging when the sun came rose. I was in the middle of wheat-fields and noticed that there was a glow around the upper part of body's shadow on the fields. At first I thought that ...
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3answers
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Conservation of energy and Doppler effect?

From what I understand, the frequency of light coming from the source moving towards an observer increases. From $ E=hv $ , this implies increase in energy of photon. What really is confusing, is ...
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6answers
4k views

Why is Light invisible?

Why can't we see light? The thing which makes everything visible is itself invisible. Why is it so?
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2answers
1k views

If light rays obey to the wave equation, why can they be thought as straight lines?

I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object ...
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4answers
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How many percent of the visible light reaching the Earth are from other stars than the Sun?

How many percent of the whole visible light reaching the Earth are from other stars than the Sun? Is it maybe 0,5 - 1% or is my guess already too much? I am interested mainly in visible light, but ...
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2answers
2k views

Is it possible to charge photons

For example there are anti-particles to every particle we know, Similary in some sense, is there a possibility that we can charge photons..if not what are the reasons and has there been any attempt ...
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3answers
2k views

Is there a light source that emits all wavelengths of visible light at the same time?

Many light sources like LEDs and lasers only emit a single wavelength of light. Is there a light source that emits all wavelengths of visible light at the same time?
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4answers
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Why is the speed-of-light “the upper limit” rather than the speed of “particle type X”?

Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics. Could it be that there exists an upper limit on ...
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2answers
1k views

Would using Cherenkov radiation for lighting be feasible?

Could Cherenkov radiation be used for general illumination, for example, to replace LEDs, light bulbs etc? I.e. are there, or could there be, methods to produce substantial amount visible light with ...
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1answer
1k views

Distribution of star colours in a galaxy

I'm trying to randomly generate a representation of a galaxy. I have some Idea on the spatial distribution of stars within a galaxy, and I can find plenty of material on the colour of stars, but ...
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2answers
3k views

Squinting at street lights

Simple question, I've always wanted to know the answer to this. Why do you see a pair of lines radiating out from street lights when your squint at them? I can't think of a better way of describing ...
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2answers
306 views

Which of these theories on why light slows in media are true?

This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity. It's a ...
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5answers
1k views

Superposition of electromagnetic waves

The superposition of two waves is given by $$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$ For sound waves, this ...
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2answers
88 views

Why is reflected light polarised?

Why is reflected light polarised? I have learnt about Brewster's angle, and how at a particular angle all light reflected is polarised, but do not understand why. Is this something that could be ...
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5answers
764 views

Will freely rotatable polarizers align?

Will two freely rotatable linear polarizers (placed in sequence and at some angular offset less than, say, 45 degrees) eventually align if you shine (plenty of) unpolarized light at the first one? If ...
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6answers
34k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...